Photosensitive composition for manufacturing optical waveguide, production method thereof and polymer optical waveguide pattern formation method using the same

ABSTRACT

A photosensitive composition for optical waveguides comprising of an organic oligomer, a polymerization initiator and a crosslinking agent, the organic oligomer being a silicone oligomer represented by the following formula (1), wherein X denotes hydrogen, deuterium, halogen, an alkyl group or an alkoxy group; m is an integer from 1 to 5; x and y represent the proportion of respective units, and neither x nor y is 0; and R1 denotes a methyl, ethyl, or isopropyl group; a production method thereof, and a polymer optical waveguide pattern formation method using the same.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 09/409,078, filed Sep. 30, 1999 now U.S. Pat. No. 6,537,723, thecontents of which are incorporated in their entirety herein.

This application is based on Patent Application No. 10-283142 filed onOct. 5, 1998 in Japan, the content of which is incorporated hereinto byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polymer optical waveguide patternformation method using a polymer material. The present invention can beutilized in various optical waveguides, optical integrated circuits,optical wiring boards and the like which are used in general optical andmicro-optical areas and in optical communication or optical informationprocessing areas.

2. Description of the Related Art

Pushed by market requirements and national policy, construction ofhigh-capacity optical fiber networks and preparation of FTTX (fiber tothe X point) are being promoted. That is, WDM-MUX/DEMUX (WavelengthDivision Multiplexing-Multiplexer/Demultiplexer) using an arrayedwaveguide grating (AWG) as a key device has reached a practicallyapplicable level, and a high-capacity and high-expandability network hasbecome available. The demands of the market are expected for changesinto optical networks of large-scale nodes, local networks, and variousLAN systems in addition to transmission lines and MUX/DEMUX, in thefuture.

Polymer material is an optically isotropic amorphous material of whichoptical propagation loss is low as is inorganic glass. Application ofpolymer material to passive optical circuits is expected to bepromising. Further, utilizing its thermo-optic (TO) constant, which isan order of magnitude greater than glass, polymer material has begun tobe employed as a waveguide material to fabricate TO switches and thelike. Specific waveguide materials can include acrylic polymer, acrylicresin, polyimide, silicone resin, epoxy resin, polycarbonate and thelike. Various characteristics are required for waveguide materials.Among them, transparency, heat stability, optical isotropy, andprocessability are particularly important characteristics.

Most polymer materials are highly transparent in the visible region. Onthe other hand, overtone of vibration absorption of carbon-hydrogen bond(such as hydrocarbon skeleton) or oxygen-hydrogen bond (such as hydroxygroup) causes decrease in transparency in the near infrared region,which is considered as communication wavelength region. Therefore, afluorocarbonization of the basic skeleton and introduction of siloxaneskeleton are being attempted.

A rigid polyimide skeleton, resilient siloxane skeleton, and bridgedstructure formed by heat or light are being employed to improve heatstability.

A component having optical anisotropy such as aromatic ring should notbe oriented in order to improve optical isotropy. However, heatstability and optical isotropy are difficult to realize simultaneouslybecause the rigid or resilient skeleton to improve the heat stability asdescribed above promotes orientation of molecule.

When optical waveguides are fabricated, the processability primarilyindicates formability of core-clad layer structure. When a highmolecular-weight polymer material is spin-coated from a solution, anintermixing between core and clad layer tends to occur, which is often aproblem in waveguide processability. On the other hand, when a lowmolecular-weight oligomer is spin-coated and then bridged by light orheat, since the bridged polymer film becomes insoluble in a solvent,intermixing can be prevented. As a result, it tends to have a superiorprocessability.

Polymer materials are suitable for producing large-area opticalwaveguides because they are readily formed into thin films by a spincoating method or a dipping method. Further, according to such a method,since film is not formed at high temperatures, it has an advantage thatoptical waveguides can be constructed on substrates such assemiconductor substrates or plastic substrates which are difficult to beheat-treated at high temperatures. Still further, it is possible toproduce a flexible optical waveguide utilizing the flexibility ortenacity of polymer materials. For such reasons, it is expected toproduce optical waveguide parts in large quantity and at low cost byusing polymer optical materials: such optical waveguide parts includeoptical integrated circuits used in the field of optical communications,optical wiring boards used in the field of optical informationprocessing and the like.

Polymer optical materials have been considered to have problems in termsof environmental resistance such as heat stability or moistureresistance. However, a material with heat stability by introducing anaromatic group such as benzene ring and/or an inorganic polymer isdisclosed recently, for example, in Japanese Patent ApplicationLaid-open No. 3-43423(1991). Polymer materials have advantageouscharacteristics in thin film formation and heat treatment process asdescribed above, and problems such as in heat stability or moistureresistance are being improved.

The following methods are reported to form polymer optical waveguides,such as a photo-locking or selective photo-polymerization method(Kurokawa et al., Applied Optics vol. 17, p. 646, 1978) in which amonomer is included in a polymer material, the polymer material isreacted partly with the monomer by irradiation with light to produce arefractive index difference between the irradiated part and unirradiatedpart; an applied method such as lithography or etching used insemiconductor processing (Imamura et al., Electronics Letters, vol. 27,p. 1342, 1991); and a method using a photosensitive polymer or resistwhich is sperior in simplicity and mass production adaptability(Trewhella et al., SPIE, vol. 1177, p. 379, 1989). Further, a waveguideproduction method in which a photopolymerization initiator is added toan epoxy oligomer or the like, and a core is formed by irradiation oflight, and then an uncured part is removed, is disclosed in JapanesePatent Application Laid-open No. 10-253845(1998).

As described above, there are many requirements for polymer materialsused for optical waveguides. Among them, there are some requirementssuch as heat stability and optical isotropy. They are based on ideascontrary to each other in the molecular design. Consequently, there isvery few material which meets all of such requirements at the same time.However, such a material is not absolutely unavailable, and there is anexample of a thermosetting silicone resin: the compatibility betweentransparency and heat stability can be established by using a laddersiloxane skeleton; optical isotropy can be secured by random thermalcrosslinking; and core-clad layer structure formation can be facilitatedby thermally crosslinking a film formed with an oligomer and making thefilm insoluble in solvents.

As described above, silicone resin has superior characteristics as anoptical waveguide material, but processability has not beensatisfactory. For example, dry etching in the production of a core ridgerequires a long time and a plurality of processes, like an inorganicmaterial such as glass or semiconductor. Therefore, as to silicone resinfor optical waveguide, as already realized in certain polymers, that is,a photocurable resin, it is desirable that the core-ridge can bedirectly produced by a simple method in which the resin isphoto-crosslinked and an unreacted part is washed out by a solvent.

Normally, as a method for providing a silicone oligomer with aphotocurability, a method is used in which epoxy group or vinyl ethergroup or radical polymerizable acrylic group is introduced into thesilicone oligomer itself by covalent bond. However, in these methods,bond between side chains by crosslinking is dominant rather thansiloxane bond, which generates problems not only in heat stability butalso in an inevitable increase in optical propagation loss due toincrease in ratio of hydroxy group in the case of epoxy or due toincrease in ratio of hydrocarbon in the case of vinyl ether or acrylics.

SUMMARY OF THE INVENTION

In view of such circumstances relating to a polymer material for anoptical waveguide, the present invention relates to a photosensitivecomposition for producing an optical waveguide and a polymer opticalwaveguide pattern formation method. The present invention provides anoptical waveguide material consisting of a polymer material with aphotosensitivity. This invention discloses simple and high-speedwaveguide formation with outstanding performance in all of transparency,heat stability, optical isotropy and processability.

When an aromatic group such as benzene ring is contained in a molecularstructure in order to improve the heat stability, the aromatic groupsuch as benzene ring is oriented to manifest an optical anisotropythereby increasing birefringence. Because an optical waveguide or thelike produced using such a material has a polarization dependence, itsoutput characteristic is changed by variation of polarization plane evenwhen the intensity of incident light is constant. In particular, this isa problem when the waveguide is actually used as a single mode opticalwaveguide. To eliminate the polarization dependence, it is necessary touse in combination with a polarizer. However, this method has adisadvantage because it makes the construction of the optical devicesubstantially complicated.

The polymer optical waveguide pattern formation method according to thepresent invention has been made in view of such present circumstances.The object of the present invention is to form a polymer opticalwaveguide pattern which is simple and suitable for mass production andcan be easily connected with optical components by using a reactiveoligomer which has simple pattern formation ability, superior heatstability and moisture resistance, small birefringence, and superiorprocessability.

Therefore, in a first aspect of the present invention, a photosensitivecomposition for optical waveguides comprises: an organic oligomer, apolymerization initiator and a crosslinking agent, in which the organicoligomer is a silicone oligomer represented by the following formula(1):

wherein X denotes hydrogen, deuterium, halogen, an alkyl group or analkoxy group; m is an integer from 1 to 5; x and y designate theproportion of respective units, and neither x nor y is 0; and R₁ denotesa methyl, ethyl, or isopropyl group.

Here, the photosensitive composition for optical waveguides may becationic photopolymerizable, and the crosslinking agent capable ofgreatly activating the photopolymerizability of the silicone oligomer asa main component of the composition may have at least an epoxy moiety oran alkoxysilane moiety in the molecule.

In a second aspect of the present invention, a photosensitivecomposition for optical waveguides comprises: an organic oligomer and apolymerization initiator, in which the organic oligomer is a siliconeoligomer represented by the following formula (2):

wherein X₁ and X₂ may be the same as or different from each other, andrepresent hydrogen, deuterium, halogen, an alkyl group or an alkoxygroup; m is an integer from 1 to 5; and Z denotes an epoxy group shownin the following formula (I) or (II):

wherein x and y designate the proportion of respective units; and y issmaller than x and may be 0.

In a third aspect of the present invention, a photosensitive compositionfor optical waveguides comprises: an organic oligomer, a polymerizationinitiator and a crosslinking agent, in which the organic oligomer is asilicone oligomer represented by the following formula (3):

wherein X denotes hydrogen, deuterium, halogen, an alkyl group or analkoxy group; m is an integer from 1 to 5; x and y designate theproportion of respective units, and neither x nor y is 0; and R₁ and R₂may be the same as or different from each other, and denote a methyl,ethyl, or isopropyl group.

Here, the photosensitive composition for optical waveguides is cationicphotopolymerizable, and the crosslinking agent capable of greatlyactivating the photopolymerizability of said silicone oligomer as a maincomponent of the composition may have at least an epoxy moiety or analkoxysilane moiety in the molecule.

In a fourth aspect of the present invention, a photosensitivecomposition for optical waveguides comprises: an organic oligomer and apolymerization initiator, in which the organic oligomer is a siliconeoligomer represented by the following formula (4):

wherein X denotes hydrogen, deuterium, halogen atom, alkyl or alkoxygroup; m is an integer from 1 to 5; x and y designate the proportion ofrespective units, and neither x nor y is 0; and R₁ and R₂ may be thesame as or different from each other and denote a methyl, ethyl, orisopropyl group.

In a fifth aspect of the present invention, a photosensitive compositionfor optical waveguides comprises: an organic oligomer and apolymerization initiator, in which the organic oligomer is a oligomerrepresented by the following formula (5):

wherein R₁ and R₂ may be the same as or different from each other anddenote hydrogen, halogen, an alkyl group, an alkoxy group or atrifluoromethyl group; X₁, X₂ and X₃ may be the same as or differentfrom each other, and denote a connection group including at least oneselected from the group consisting of an alkylene, alkyleneoxy,oxyalkylene and aromatic group; and Y denotes a polymerizationactivating group.

In a sixth aspect of the present invention, a photosensitive compositionfor optical waveguides comprises: an organic oligomer and apolymerization initiator, in which the organic oligomer is a oligomerrepresented by the following formula (6):

wherein R₁ and R₂ may be the same as or different from each other, anddenote hydrogen, halogen, an alkyl group, an alkoxy group or atrifluoromethyl group; X₁, X₂ and X₃ maybe the same as or different fromeach other, and denote a connection group including at least oneselected from the group consisting of an alkylene, alkyleneoxy,oxyalkylene and aromatic group and including at least one OH group; andY denotes a polymerization activating group.

In a seventh aspect of the present invention, a method of producing theabove photosensitive composition for optical waveguides comprising thesteps of: heating a silicone oligomer and a crosslinking agent in thepresence of a solid catalyst; and filtering the solid catalyst,concentrating filtrate, and further adding a polymerization initiator.With this method, initiation of optical crosslinking is remarkablyimproved.

In a eighth aspect of the present invention, a method of forming apolymer optical waveguide pattern, comprising the steps of: applying anddrying the above photosensitive composition for optical waveguides;irradiating said resultant photosensitive composition thin film foroptical waveguides with light through a mask; and directly forming acore-ridge pattern by wet etching said photosensitive composition thinfilm. With this method, a waveguide ridge pattern having a sharp andsmooth wall surface can be simply formed without using dry etching orthe like.

The inventors have found that these reactive oligomers have a simplepattern formability and are capable of forming a polymer opticalwaveguide pattern which has superior heat stability and moistureresistance, small birefringence and is easy to connect to opticalcomponents, and accomplished the present invention.

Specifically, the present invention is capable of forming a waveguideridge pattern having a sharp and smooth wall surface by curing a film byirradiation with light and developing by an appropriate solvent.Further, although it has been very difficult to perform waveguideprocessing in a thick film polymer with material in prior art, thepresent invention can easily process the waveguide even with a thickfilm. Still further, with the present invention, birefringence of thephotocured of liquid oligomer is reduced to less then 1×10⁻³, andpolarization dependence can be reduced to less than the tolerance limit.Yet further, by controlling the molecular weight of the polymer opticalmaterial, an appropriate viscosity suitable for the thin film formationprocess can be obtained.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional view illustrating a process for producing thepolymer optical waveguide according to the present invention, showing astate in which a lower clad layer and a core layer successivelylaminated on a substrate;

FIG. 1B is a sectional view illustrating a process for producing thepolymer optical waveguide according to the present invention, showing astate in which curing light is irradiated through a mask provided on thelaminate;

FIG. 1C is a sectional view illustrating a process for producing thepolymer optical waveguide according to the present invention, showing astate in which an unirradiated is removed;

FIG. 1D is a sectional view illustrating a process for producing thepolymer optical waveguide according to the present invention, showing astate in which an optical waveguide is completed by covering the corepart formed in FIG. 1C to form a clad.

DETAILED DESCRIPTION OF THE INVENTION

The present invention which solves the problems described above in theprior art is to provide silicone resin, epoxy resin, and acrylic resinwith photocurability without deteriorating transparency, heat stabilityand optical isotropy characteristic of such resins which are capable ofdirectly forming a core-ridge.

In the present invention, a photosensitive substance is formed in layeron a substrate or a clad layer. This photosensitive substance contains areactive oligomer and a photopolymerization initiator and may furthercontain a crosslinking agent.

The reactive oligomer used in the present invention is an epoxy-typeoligomer, silicone-type oligomer or an acrylic-type oligomer.Specifically, the oligomer is a compound represented by one of aboveformulae (1) to (6), and these oligomers may be mixed.

Advantages that the photosensitive substance used in the presentinvention is a reactive oligomer are:

1) Because the state of the polymer material before curing can be madevery homogeneous, it has superior optical transmission characteristic inthe ultraviolet region or visible region, and has a sufficientresolution even when the film formed by curing is thick,

2) Because the state of the polymer material before curing is anoligomer, leveling is possible even when the substrate or the like hasirregular parts, and since the oligomer penetrates into every part, filmformation suitable for various shapes is possible,

3) Because the oligomer is randomly connected and cured, the curedmaterial is small in birefringence.

Polymerization of the epoxy oligomer used in the present invention isperformed by bonding and crosslinking by UV-irradiation between epoxy oralkoxy group and hydroxy group contained in the epoxy oligomer. In orderto effect the crosslinking reaction efficiently and sufficiently, it isdesirable to add a photopolymerization initiator. When thephotosensitive substance contains a crosslinking agent, polymerizationmay be performed by bonding and crosslinking by UV-irradiation betweenepoxy or alkoxy group and hydroxy group contained in the crosslinkingagent and epoxy oligomer material.

A silicone oligomer inherently has a property to proceed crosslinking inthe presence of a cationic photopolymerization initiator which isso-called a acid generator. Therefore, optical crosslinking is possiblein principle under a specific condition even with a combination of onlya silicone oligomer and a cationic photopolymerization initiator.

However, according to intensive studies conducted by the inventors, itis very rare that sufficient crosslinking is actually achieved by acombination of only a silicone oligomer and a cationicphotopolymerization initiator. In addition, the higher the molecularweight of the oligomer, the more crosslinking tends to proceed, howeverrepeatability is poor and the effect is insufficient. Furthermore, thismethod can not be a general-purpose technique since an increase inmolecular weight of the material itself is difficult when composition ofsubstituent is rich in aromatic groups.

Next, the inventors have attempted a method in which a cationicphotopolymerization initiator is added to silicone oligomer to form afilm on a substrate, then the film is heat-treated to increase themolecular weight, and then the film is irradiated with light to cure.Sufficient crosslinking is rarely achieved depending on the type ofsilicone oligomer and heating condition, however, in most cases,crosslinking is insufficient and there are problems in repeatability asin the above-described cases.

Finally, the inventors have found that desired photocurability can beachieved by a method in which a crosslinking agent with a remarkablefunction as a polymerization coinitiator is added as a third componentin addition to silicone oligomer and a cationic photopolymerizationinitiator. Addition of a silane coupling agent (crosslinking agent) tothe photosensitive composition may be used, for example, for the purposeof increasing adhesiveness when the photosensitive composition is cured.This is to achieve close adhesion between the cured material and amaterial contacting the cured material by containing a crosslinkingagent in the photo-cured composition to produce siloxane between boththe materials. Therefore, such purpose is substantially different fromthe use as the polymerization coinitiator in the present invention. Inthe present invention, attention is given to the fact that thephotosensitive composition for optical waveguides includes mainly asilicone oligomer. The crosslinking agent is added for the purpose thatthe agent selectively reacts with the silicone oligomer by irradiationwith light in the presence of an acid generator to effectively progressan increase in molecular weight in the initial stage ofphotopolymerization. Further, addition of a polymerization coinitiatorin the present invention has an effect for enhancing plasticity of theentire composition and promoting progress of polymerization reactionunder irradiation.

This method is found to provide sufficient crosslinking as compared withthe above-described molecular weight control method or pre-baking methodwithout being affected by the structure of silicone oligomer, high inrepeatability, and can be widely applied to photo-crosslinking ofsilicone oligomer. Crosslinking agents particularly effective aspolymerization coinitiators can include the compounds represented by ageneral formula (7). More specifically,γ-glycidoxypropyl-triethoxysilane represented by structural formula (8),1,2-bis (triethoxysilyl) ethane, 1,4-bis(triethoxysilyl) benzene,1,6-bis(triethoxysilyl) ethanehexane, and bi-functional epoxy compoundsrepresented by formulae (9), (10), (11) and (12) and the like can beexemplified.

A-R-A′  (7)

in the above formula, A and A′ are independently selected by one of thefollowing three types of structure.

In addition to the above, typical crosslinking agents effective aspolymerization coinitiators for silicone oligomer are those whichundergo ring opening or dehydration condensation by proton supply fromthe cationic photopolymerization initiator such as epoxy compounds,silane coupling agent, silanol compounds, and alkoxy compounds,including alicyclic epoxy of bifunctional or more other than theabove-described ones, (3-glycidoxypropyl) trimethoxysilane,(3-glycidoxypropyl) methyldiethoxysilane, and diphenylsilanediol.Examples of other silane coupling agents can includeaminopropyltriethoxysilane,tridecafluoro-1,1,2,2,-tetrahydro-octyltriethoxysilane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-bis[β-(aminoethyl)]-γ-aminopropylmethyldimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane,γ-methacryloxypropyltrimethoxysilane,N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyl-trimethoxysilanehydrochloride, methyltrimethoxysilane, methyltriethoxysilane,vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane,hexamethyldisilazane, γ-anilinopropyltrimethoxysilane,vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl) propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane,γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane,dimethyldichlorosilane, trimethylchlorosilane, vinyltriethoxysilane,benzyltrimethylsilane, vinyltris(2-methoxyethoxy) silane,γ-methacryloxypropyltris(2-methoxyethoxy) silane,β-(3,4-epoxycyclohexyl) ethyltrimethoxysilane,γ-ureidopropyltriethoxysilane, γ-isocyanurpropyltriethoxysilane,n-octyltriethoxysilane and the like.

In the present invention, polymerization of the silicone oligomermaterial includes polymerization by a reaction of a crosslinking agentwith the silicone oligomer. Typical crosslinking agents used here caninclude azide compounds such as azidepyrene, bisazide compounds such as4,4′-diazidebenzalacetone, 2,6-di-(4′-azidebenzal) cyclohexanone,2,6-di-(4′-azidebenzal)-4-methylcyclohexanone, diazo compounds and thelike.

Polymerization of acrylic oligomer is performed by a reaction of thecrosslinking agent with the acrylicoligomer. As the crosslinking agentused here, carbonyl compounds such as diphenyltriketonebenzoin,benzoinmethylether, benzophenone, acetophenone, and diacetyl; peroxidessuch as benzoyl peroxide; azo compounds such as asobis-isobutyronitrile;azide compounds such as azidepyrene; bisazide compounds such as4,4′-diazidebenzalacetone, 2,6-di-(4′-azidebenzal) cyclohexanone,2,6-di-(4′-azidebenzal)-4-methylcyclohexanone, and diazo compounds areexemplified as typical ones.

The photopolymerization initiator used in the present invention is notspecifically limited if it is generally used as a photopolymerizationinitiator, and typical cationic photopolymerization initiators includesulfonium salt, osmium salt, antimonium salt and the like. Specifically,preferred cationic photopolymerization initiators include but are notlimited to N-benzyl-4-benzoylpyridinium hexafluoroantimonate,N-(3-methyl-2-butenyl)-2-cyanopyridinium hexafluorophosphate,ρ-chlorobenzenediazonium hexafluorophosphate, diphenyliodoniumhexafluorophosphate, and tris(ethylacetoacetato)aluminum. The amount ofthe crosslinking agent to be added is as small as 1 to 2% and not morethan several %.

The optical waveguides produced using the photosensitive compositionaccording to the present invention can be released from the nearinfrared absorption effect inherent to the crosslinking agent, andmaintains the characteristic of optical propagation loss, as is, in thecommunication wavelength band intrinsic of silicone resin.

Normally, to provide silicone oligomer with photocurability, epoxy orvinyl ether or acrylic group is introduced into the silicone oligomeritself by covalent bond. However, the amount of crosslinking agent usedin this case is converted to the amount more than about 50 times aslarge as the present invention. Thus, the bond between side chains bycrosslinking is dominant rather than the strong siloxane bond, whichgenerates not only problems such as heat stability but also aninevitable increase in optical propagation loss due to increase inproportion of hydroxy group in the case of epoxy and increase inproportion of hydrocarbon in the case of vinyl ether or acrylic. Thatis, formation of a core-ridge directly by light without deterioratingthe heat stability and low-loss characteristic incommunication-wavelength band specific to silicone resin is possible forthe first time using the photosensitive composition for opticalwaveguides according to the present invention.

A method for producing an optical waveguide using a reactive oligomermaterial according to the present invention will be described withreference to FIGS. 1A to 1D. FIGS. 1A to 1D are schematic sectionalviews illustrating processes of forming an optical waveguide accordingto the present invention.

In the present invention, the reactive oligomer is coated on a substrateor a clad, after position registration, the coating is irradiated withUV light through a mask or directly, and an unirradiated portion isdissolved away with a solvent to form a waveguide ridge pattern.

Specifically, as shown in FIG. 1A, a lower clad forming resin layer 2 isformed on a substrate 1, and a core part forming photosensitivesubstance layer 3 is formed thereon. Next, as shown in FIG. 1B, a mask 4having a pattern of core part shape is placed on the photosensitivesubstance layer 3, and irradiated with UV light 5 through the mask 4.This cures only the core part 6 of the photosensitive substance layer 3.After that, a UV light unirradiated portion of the photosensitivesubstance layer 3, is dissolved out to form a ridge pattern of the corepart 6 as shown in FIG. 1C. The same photosensitive resin as the cladpart forming resin layer 2 is coated so that the core part 6 is buriedthereby forming a clad part 7 as shown in FIG. 1D. The thus producedoptical waveguide has superior solvent resistance, is small inpolarization dependence because the material used is small inbirefringence, low in propagation loss, and has superior heat stabilityand moisture resistance.

EXAMPLES

The present invention will be described in further detail with referenceto examples, however, the present invention is not limited to theseexamples.

Example 1

Phenyltrichlorosilane (211.5 g) and methyltrichlorosilane (36.3 g) weredissolved in 1 liter of anhydrous tetrahydrofuran, and 3 equivalents ofwater (67.5 g) was slowly added dropwise to the solution so that theliquid temperature does not increase. After that, 315 g of sodiumhydrogencarbonate was added while agitating the reaction liquid. Afterthe completion of carbon dioxide gas evolution, agitation was continuedfor further 1 hour. Next, the reaction liquid was filtered, thentetrahydrofuran was distilled out by a rotary evaporator to give acolorless, transparent viscous liquid. Further, this liquid was vacuumdried to give an oligomer A. The molecular weight of resulting oligomerA was measured by GPC and the result was Mw==3300, Mn=1500.

Next, a photosensitive substance A was prepared which comprises 50 g ofoligomer A, 25 g of UV resin, 2 weight % of N-benzyl-4-benzoylpyridiniumhexafluoroantimonate as a photopolymerization initiator and 25 g ofmethylisobutylketone as a solvent. An optical waveguide using thephotosensitive substance A in the core, and an ultraviolet curable resin(UV resin) in the clad was produced as shown in FIGS. 1A to 1D. First,the UV resin was applied to a silicon substrate by a spin coating methodto form a layer. At this moment, the rotational speed of the spin coaterwas adjusted so that the film thickness is 15 μm. The formed layer wasirradiated with UV light of 7000 mJ/cm², and then heated at 90° C. for30 minutes to form a lower clad layer 2. Next, the photosensitivesubstance A was applied by the spin coating method to form a core partformation layer. In this case, the rotational speed of the spin coaterwas adjusted so that the film thickness is 8 μm. At this moment, nointermixing was noted between the lower clad layer and the core partformation layer. The formed core part formation layer was heated at 120°C. for 10 minutes to remove the solvent. A mask 4 having a core partpattern to provide a core width of 8 μm was placed on the core partformation layer, and UV light of 7000 mJ/cm² was irradiated through themask. After that, the core part 6 was patterned by heating at 120° C.for 2 minutes. Next, development was performed using a 1:1 mixed solventof methylisobutylketone and isoproylalcohol to remove a UV lightunirradiated portion. The developed layer was heated at 120° C. for 30minutes to form a core ridge. The same UV resin used for the lower cladwas applied onto it and then photocured as the lower clad to produce aburied type channel optical waveguide as shown in FIG. 1, which has astructure with the core part 6 buried in the clad part 7. In this case,the thickness of the upper clad is 8 μm from the upper surface of thecore.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw, and measured for propagation loss which showed 1.0 dB/cm atwavelength 1.3 μm, and 1.2 dB/cm or less at wavelength 0.633 μm.Further, this optical propagation loss of the waveguide was unchangedfor more than 1 month under the condition of 75° C./90% RH.

Example 2

A photosensitive substance B was prepared which comprises 50 g of theoligomer A produced in Example 1, 1 g of (3-glycidoxypropyl)trimethoxysilane as a crosslinking agent, 2 weight % ofN-benzyl-4-benzoylpyridinium hexafluoroantimonate as aphotopolymerization initiator, and 25 g of methylisobutylketone as asolvent.

Using the same procedure as in Example 1 except that the photosensitivesubstance B was used in place of the photosensitive substance A as acore part forming photosensitive substance, a buried type channeloptical waveguide comprising a core-clad layer structure as shown inFIG. 1D was produced. In this case, the thickness of the upper clad is 8μm from the upper surface of the core. Further, no intermixing was notedbetween the lower clad layer and the core part formation layer.

As in Example 1, the resulting optical waveguide was cut to a length of5 cm by a dicing saw, and measured for optical propagation loss whichshowed 0.5 dB/cm at wavelength 1.3 μm, and 0.8 dB/cm or less atwavelength 1.55 μm. Further, this optical propagation loss of thewaveguide was unchanged for more than 1 month under the condition of 75°C./90% RH.

Example 3

Oligomer B was produced using the same procedure as in Example 1 exceptthat deuterated phenyltrichlorosilane was used in place ofphenyltrichlorosilane in the production of oligomer A in Example 1, anda photosensitive substance C was produced using the same procedure as inExample 2 except that oligomer B was used in place of oligomer A. Next,a buried type channel optical waveguide of core diameter 8 μm×8 μm wasproduced by the same process as in Example 2.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw, and measured for optical propagation loss which showed 0.1 dB/cm atwavelength 1.3 μm, and 0.5 dB/cm or less at wavelength 1.55 μm. Further,this optical propagation loss of the waveguide was unchanged for morethan 1 month under the condition of 75° C./90% RH.

Examples 4 to 11

Using quite the same procedure as in Example 3, eight types of opticalwaveguide differing in compositional ratio of silicone oligomer sidechain of the core, crosslinking agent and initiator were produced. Therespective optical waveguides were measured for optical propagationloss, and the results of measurement are shown in Table 1 comparing withthe results of Example 1 to 3.

TABLE 1 optical propagation loss of respective waveguides (1)

Structure of silicone cross- oligomer(1) used linking polymerizationExample in core agent initiator loss (dB/cm) 1 X = H, R₁ = CH₃ NilN-benzyl-4-benzoylpyridinium 1.0(at 1.31 μm) x = 0.5, y = 0.5 hexafluoroantimonate (13) 2 X = H, R₁ = CH₃ (8) (13) 0.5(at 1.3 μm) x = 0.95, y =0.05 0.8(at 1.55 μm) 3 X = D, R₁ = CH₃, (8) (13) 0.1(at 1.31 μm) x =0.95, y = 0.05 0.5(at 1.55 μm) 4 X = D, R₁ = CH₃, (8) (13) 0.2(at 1.31μm) x = 0.5, y = 0.5 1.0(at 1.55 μm) 5 X = D, R₁ = CH₃, (8) (13) 0.3(at1.31 μm) x = 0.3, y = 0.7 1.2(at 1.55 μm) 6 X = D, R₁ = CH₃, (9)N-(3-methyl-2-butenyl)-2-cyanopyridinium 0.1(at 1.3l μm) x = 0.95, y =0.05 hexafluorophosphate 0.5(at 1.55 μm) (14) 7 X = D, R₁ = CH₃, (9)(14) 0.2(at 1.31 μm) x = 0.5, y = 0.5 1.0(at 1.55 μm) 8 X = D, R₁ = CH₃,(9) (14) 0.3(at 1.31 μm) x = 0.3, y = 0.7 1.2(at 1.55 μm) 9 X = H, R₁ =CH₃, (10) p-chlorobenzene 0.3(at 1.31 μm) x = 0.95, y = 0.05 diazonium1.0(at 1.55 μm) hexafluorophosphate 10  X = Cl, R₁ = C₂H₅, (11)diphenyliodonium 0.3(at 1.31 μm) x = 0.95, y = 0.05 hexafluorophosphate0.8(at 1.55 μm) 11  X = OCH₃, R₁ = C₃H₇ (12) tris(ethylacetoaceta 0.5(at1.31 μm) x = 0.95, y = 0.05 to)aluminum 1.5(at 1.55 μm)

Example 12

A photosensitive substance D was prepared from 100 weight % of liquidoligomer having the following structural formula (15) (where z=0 to 2)and 2 weight % of N-benzyl-4-benzoylpyridinium hexafluoroantimonate as aphotopolymerization initiator.

Epoxy resin having a thickness of 100 μm was formed on a substrate. Thisepoxy resin had a refractive index of 1.52 at wavelength 1.55 μm. Next,the photosensitive substance D was applied to the epoxy resin layer byspin coating method to form a photosensitive substance layer. Afterthat, the layer was irradiated with UV light through a mask having awaveguide pattern of core part shape. In this case, irradiation amountof UV light was 2000 mJ/cm². When the layer was developed by anisopropanol solution, a UV light unirradiated portion of thephotosensitive substance layer was dissolved, and only a UV lightirradiated portion of the cured liquid epoxy oligomer was remained toform a ridge pattern of core part shape. The refractive index of thecore part after curing was 1.525 at wavelength 1.55 μm. After that, thisridge pattern was coated with an epoxy resin adjusted to provide arefractive index at photocuring of 1.52 at wavelength 1.55 μm, and curedto produce an optical waveguide where the core is buried in the clad asshown in FIG. 1D. Thus, a single mode channel waveguide (core diameter 8μm×8 μm, Δn=0.3%) having a clad comprising epoxy resin of refractiveindex 1.52 and a core comprising UV-cured epoxy resin of refractiveindex 1.525 was produced.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw, and measured for optical propagation loss which was 1.5 dB or lessat wavelength 1.3 μm, and 3.0 dB or less at wavelength 1.55 μm.Polarization dependence of the optical propagation loss was 0.1 dB orless at both wavelength 1.3 μm and 1.55 μm. Further, the resultingoptical propagation loss of the waveguide was unchanged for more than 1month under the condition of 75° C./90% RH.

Example 13

A single mode channel waveguide (core diameter 8 μm ×8 μm, Δn=0.3%) wasproduced using the same procedure as in Example 12 except that aphotosensitive substance E prepared from 100 weight % of liquid siliconeepoxy oligomer (desirably having a molecular weight of 1000 to 10000)represented by the following structural formula (16) and 2 weight % ofN-benzyl-4-benzoylpyridinium hexafluoroantimonate as aphotopolymerization initiator was used in place of the photosensitivesubstance D.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw, and measured for optical propagation loss which showed 1.0 dB orless at wavelength 1.3 μm, and 1.5 dB or less at wavelength 1.55 μm.Polarization dependence of the optical propagation loss was 0.1 dB orless at wavelength both 1.3 μm and 1.55 μm. Further, the opticalpropagation loss of the waveguide was unchanged for more than 1 monthunder the condition of 75° C./90% RH.

Example 14

A single mode channel waveguide (core diameter 8 μm ×8 μm, Δn=0.3%) wasproduced using the same procedure as in Example 12 except that aphotosensitive substance F prepared from 100 weight % of liquid siliconeoligomer represented by the following structural formula (17) and 2weight % of N-benzyl-4-benzoylpyridinium hexafluoroantimonate as aphotopolymerization initiator was used in place of the photosensitivesubstance D.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw, and measured for optical propagation loss which was 1.5 dB or lessat wavelength 1.3 μm, and 3.0 dB or less at wavelength 1.55 μm.Polarization dependence of the optical propagation loss was 0.1 dB orless at wavelength both 1.3 μm and 1.55 μm. Further, the opticalpropagation loss of the waveguide was unchanged for more than 1 monthunder the condition of 75° C./90% RH.

Next, a multi-mode optical waveguide (depth 40 μm, width 40 μm, Δn=1%)was produced using the same procedure as in Example 1 except that theabove photosensitive substance F was used in place of the photosensitivesubstance A. This optical waveguide was cut to a length of 5 cm by adicing saw, and measured for optical propagation loss which was 1.0 dBor less at wavelength 0.85 μm, 0.5 dB or less at wavelength 1.3 μm and1.0 dB or less at wavelength 1.55 μm. Polarization dependence of theoptical propagation loss was less 0.1 dB or less. Further, the opticalpropagation loss of the waveguide was unchanged for more than 1 monthunder the condition of 75° C./90% RH.

Examples 15 to 23

Using quite the same procedure as in Example 14, nine types of opticalwaveguide differing in compositional ratio of silicone oligomer sidechain of the core, crosslinking agent and initiator were produced. Therespective optical waveguides were measured for optical propagationloss, and the results of measurement are shown in Table 2.

TABLE 2 Loss of optical propagation in respective waveguides (17)

Structure of silicone cross- oligomer(17) linking polymerization Exampleused in core agent initiator lost (dB/cm) 15 x = 0.95, y = 0.05 (8)N-benzyl-4-benzoylpyridinium 0.2(at 1.31 μm) hexafluoro 0.6(at 1.55 μm)antimonate (13) 16 x = 0.5, y = 0.5 (8) (13) 0.3(at 1.31 μm) 1.2(at 1.55μm) 17 x = 0.3, y = 0.7 (8) (13) 0.4(at 1.31 μm) 1.5(at 1.55 μm) 18 x =0.95, y = 0.05 (9) N-(3-methyl-2-butenyl)-2-cyano-pyridinium 0.2(at 1.31μm) hexafluorophosphate 0.6(at 1.55 μm) (14) 19 x = 0.5, y = 0.5 (9)(14) 0.3(at 1.31 μm) 1.2(at 1.55 μm) 20 x = 0.3, y = 0.7 (9) (14) 0.4(at1.31 μm) 1.5(at 1.55 μm) 21 x = 0.5, y = 0.5 (10)  p-chlorobenzene0.3(at 1.31 μm) diazonium 1.2(at 1.55 μm) hexafluorophosphate 22 x =0.5, y = 0.5 (11)  diphenyliodonium 0.3(at 1.31 μm) hexafluorophosphate1.2(at 1.55 μm) 23 x = 0.5, y = 0.5 (12)  tris(ethylaceto 0.5(at 1.31μm) acetato) aluminum 1.2(at 1.55 μm)

Example 24

A single mode channel waveguide (core diameter 8 μm ×8 μm, Δn=0.3%) wasproduced using the same procedure as in Example 12 except that aphotosensitive substance G prepared from 100 weight % of liquid siliconevinylether oligomer represented by the following structural formula (18)and 2 weight % of 2,6-di(4′-azidebenzal)-4-methylcyclohexanone as aphotopolymerization initiator was used in place of the photosensitivesubstance D.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw, and measured for optical propagation loss which was 1.5 dB or lessat wavelength 1.3 μm, and 3.0 dB or less at wavelength 1.55 μm.Polarization dependence of the optical propagation loss was 0.1 dB orless. Further, the optical propagation loss of the waveguide wasunchanged for more than 1 month under the condition of 75° C./90% RH.

Example 25

A single mode channel waveguide (core diameter 8 μm ×8 μm, Δn=0.3%) wasproduced using the same procedure as in Example 12 except that aphotosensitive substance H prepared from 100 weight % of liquid acrylicoligomer represented by the following structural formula (19) and 2weight % of diphenyltriketonebenzoin as a photopolymerization initiatorwas used in place of the photosensitive substance D.

The resulting optical waveguide was cut to a length of 5 cm by a dicingsaw and measured for optical propagation loss which was 0.5 dB or lessat wavelength 1.3 μm, and 5.0 dB or less at wavelength 1.55 μm.Polarization dependence of the optical propagation loss was 0.1 dB orless at wavelength both 1.3 μm and 1.55 μm. Further, the opticalpropagation loss of the waveguide was unchanged for more than 1 monthunder the condition of 75° C./90% RH.

Example 26

240 g of Phenyltriethoxysilane, 20 g of methyltriethoxysilane, 10 g ofwater, 100 g of isopropylalcohol, and 0.1 g of hydrochloric acid weremixed, heated under reflux for 4 hours. Then solvents and the like wereremoved under vacuum using a rotary evaporator to give 112 g ofcolorless, transparent oligomer C. 50 g of the oligomer C, 1 g of3glycidoxypropyltriethoxysilane, 7 g of water, 20 g of isopropylalcohol,2 g of ion-exchange resin (AMBERLITE IRA900 from Aldrich Co.) werecharged into a reaction vessel, heated at 80° C. for 12 hours whileagitating. The ion exchange resin was removed by filtration, and thenisopropylalcohol was removed under vacuum using a rotary evaporator togive 44 g of a colorless, transparent oily substance D.

Next, using the same procedure as above except that 253 g ofphenyltriethoxysilane and 6 g of methyltriethoxysilane were used, 110 gof colorless, transparent oligomer E was obtained, which gave 40 g of acolorless, transparent oily substance F.

Using these oily substances D and F, an optical waveguide was producedaccording to the conventional photolithographic technique using thefollowing procedure. First, the oily substance D was mixed with acationic photopolymeization initiator to give a photosensitivecomposition G for optical waveguides which was applied onto a siliconwafer by a spin coating method. In this case, the rotational speed ofthe spin coater was adjusted so that the film thickness is about 15 μm.The formed film was photocured by irradiation of UV light for 10minutes, and thoroughly cured at 150° C. to form a lower clad layer.Next, the oily substance F was mixed with a cationic photopolymerizationinitiator to give a photosensitive composition H for optical waveguides,which was applied to the above-mentioned lower clad layer, andirradiated with UV light for 10 minutes through an 8 μm wide linearmask. An uncured portion was washed out by a solvent, and thoroughlycured at 150° C. to form a rectangular core of 8 μm in width and 8 μm inheight. An upper clad was formed on it using the same procedure as thelower clad to give a buried optical waveguide. The waveguide wasmeasured for optical propagation loss at 1.55 μm band which wasconfirmed to be less than 0.5 dB/cm.

Examples 27 to 30

The oligomers shown in Table 3 were used in place of oligomer E,respectively treated with ion-exchange resin as in Example 26 to preparephotosensitive substances mixed with photopolymerization initiator.Further, a buried channel optical waveguide having core-clad layerstructure as shown in FIG. 1D was produced using the same procedure asin Example 1 except that the above treated photosensitive substance wasused in place of the photosensitive substance A as the core part formingphotosensitive substance. In this case, the thickness of the upper cladwas controlled to 8 μm. No intermixing was noted between the lower cladlayer and the core part formation layer. The results of opticalpropagation loss measurement are shown in Table 3.

TABLE 3 Loss of optical propagation in respective waveguides Structureof silicone oligomer polymerization Example used in core initiator loss(dB/cm) 27 (15) N-benzyl-4-benzoyl- 1.5 (at 1.31 μm) pyridiniumhexafluoro 3.0 (at 1.55 μm) antimonate (13) 28 (16) (13) 1.0 (at 1.31μm) 1.5 (at 1.55 μm) 29 (17) (13) 1.5 (at 1.31 μm) 3.0 (at 1.55 μm) 30(19) (13) 0.5 (at 1.31 μm) 5.0 (at 1.55 μm)

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent that changes andmodifications may be made without departing from the invention in itsbroader aspects, and it is the intention, therefore, in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit of the invention.

What is claimed is:
 1. A method of forming a polymer optical waveguidepattern, comprising the steps of: applying and drying a photosensitivecomposition for optical waveguides; irradiating said resultantphotosensitive composition thin film for optical waveguides with lightthrough a mask; and directly forming a core-ridge pattern by wet etchingsaid photosensitive composition thin film; wherein the photosensitivecomposition comprises an organic oligomer, said organic oligomer being asilicone oligomer represented by the following formula (1):

wherein X denotes hydrogen, deuterium, halogen, an alkyl group or analkoxy group; m is an integer from 1 to 5; x and y designate theproportion of respective units, and neither x nor y is 0; and R₁ denotesa methyl, ethyl, or isopropyl group; a polymerization initiator which isan acid generator; and a crosslinking agent which is a separate,independent compound from said silicone oligomer.
 2. A method of forminga polymer optical waveguide pattern as claimed in claim 1, wherein saidphotosensitive composition for optical waveguides is cationicphotopolymerizable, and said crosslinking agent is capable of greatlyactivating photopolymerizability of said silicone oligomer as a maincomponent of said composition.
 3. A method of forming a polymer opticalwaveguide pattern as claimed in claim 1, wherein said crosslinking agenthas at least an epoxy moiety or an alkoxysilane moiety in the molecule.4. A method of forming a polymer optical waveguide pattern as claimed inclaim 1, wherein said crosslinking agent is at least one compoundselected from the group consisting of the formulas (8), (9), (10), (11)and (12):


5. A method of forming a polymer optical waveguide pattern, comprisingthe steps of: applying and drying a photosensitive composition foroptical waveguides; irradiating said resultant photosensitivecomposition thin film for optical waveguides with light through a mask;and directly forming a core-ridge pattern by wet etching saidphotosensitive composition thin film; wherein the photosensitivecomposition comprises an organic oligomer, said organic oligomer being asilicone oligomer represented by the following formula (3):

wherein X denotes hydrogen, deuterium, halogen, an alkyl group or analkoxy group; m is an integer from 1 to 5; x and y designate theproportion of respective units, and neither x nor y is 0; and R₁ and R₂may be the same as or different from each other, and denote a methyl,ethyl, or isopropyl group; a polymerization initiator which is an acidgenerator; and a crosslinking agent which is a separate, independentcompound from said silicone oligomer.
 6. A method of forming a polymeroptical waveguide pattern as claimed in claim 5, wherein saidphotosensitive composition for optical waveguides is cationicphotopolymerizable, and said crosslinking agent is capable of greatlyactivating photopolymerizability of said silicone oligomer as a maincomponent of said composition.
 7. A method of forming a polymer opticalwaveguide pattern as claimed in claim 5, wherein said crosslinking agenthas at least an epoxy moiety or an alkoxysilane moiety in the molecule.8. A method of forming a polymer optical waveguide pattern as claimed inclaim 5, wherein said crosslinking agent is at least one compoundselected from the group consisting of the formulas (8), (9), (10), (11)and (12):